Playing last night, I had an experience with diplomacy that was different from what I experienced in Civ 5, Civ 4, or Civ3. I'm playing as Kavitha, and my neighbor was PAC. We were best buddies for 150 turns; 4 diplo agreements, trade routes, raised our relationship to "Allied" for much of that time. After turn 150 or so, the other smaller AIs start declaring war on each other. I can't see much reason why, unless I'm missing something. When PAC declared on someone else, I DoW'ed also, thru the alliance. I fought alongside her, killing mutual enemies. To focus on my own development, I moved the relationship down one notch to "Cooperating." She grumbled, but kept on doing her thing. PAC only had 2 cities, but she was feisty and declared on other AIs. Suddenly, 10-15 turns after I changed the relationship status, she moves from "Cooperating" to "War". WTF? I bring back my navy from the other side of the planet, chewing up the PAC navy along the way. War score over 300 in my favor -- won't talk peace. I overwhelm and puppet her second city. War score just over 1000 in my favor -- won't talk peace. I literally checked for a way to stop the war *every turn* while my forces lined up on her border. Nothing. I bombard her capital with navy and air power, and take it. Questions: What would cause an AI to (essentially) commit suicide by declaring on me? Breaking all the mutually beneficial agreements that we have in place? Is it unusual to go from "Cooperating" right to "War"? In Civ 5, they usually denounce me before declaring, and the BERT analog would seem to be lowering our relationship to "Sanctioned" Do the AIs usually start declaring on each other in the late game? They've taken each other's cities and puppeted them. Are those old grievances building up?